batman-adv: remove obsolete skb_reset_mac_header() in batadv_bla_tx()

Our .ndo_start_xmit handler (batadv_interface_tx()) can rely on having
the skb mac header pointer set correctly since the following commit
present in kernels >= 3.9:

"net: reset mac header in dev_start_xmit()" (6d1ccff6)

Therefore this commit removes the according, now redundant,
skb_reset_mac_header() call in batadv_bla_tx().
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

net/batman-adv/bridge_loop_avoidance.c

@@ -1547,9 +1547,6 @@ int batadv_bla_tx(struct batadv_priv *bat_priv, struct sk_buff *skb,
 	if (!atomic_read(&bat_priv->bridge_loop_avoidance))
 		goto allow;
 
-	/* in VLAN case, the mac header might not be set. */
-	skb_reset_mac_header(skb);
-
 	if (batadv_bla_process_claim(bat_priv, primary_if, skb))
 		goto handled;